The problem of environmental pollution is too complex and multifaceted to try to study it quickly.

Noise generally receives little attention in the media and is not considered by many to be an air pollutant. But actually it is not? Until now, a huge portion of people are unaware of the dangers of noise pollution. This is due to the fact that the problems of noise pollution in the urban environment were recognized at a scientific level relatively recently and became acute only in recent decades. We did not choose the solution path by chance. Currently, the health problem is very acute, the rapid pace of life leads not only to the growth of cities, urban agglomerations and megalopolises, industry, but also, due to the following, to environmental deterioration, disruption of the geographic human environment, and, as a rule, worsens health population

Study noise as one of the environmental pollutants;

Identify the effect of noise on the human body;

Identify measures to protect people from noise exposure

1. Types of noise and their impact on human feelings.

What is noise? Based on previously acquired knowledge from the physics course, students can give

Noise is a random mixture of sounds of different pitches (frequencies). The unit of measurement is 1 dB = 10 Lg.

Man has always lived in a world of sounds and noise. Sound refers to such mechanical vibrations of the external environment that are perceived by the human hearing aid (from 16 to 20,000 vibrations per second). Vibrations of higher frequencies are called ultrasound, and vibrations of lower frequencies are called infrasound. Noise is loud sounds merged into a discordant sound.

The noise level is measured in units expressing the degree of sound pressure - decibels. This pressure is not perceived infinitely. A noise level of 20-30 decibels (dB) is practically harmless to humans; it is a natural background noise. As for loud sounds, the permissible limit here is approximately 80 decibels. A sound of 130 decibels already causes pain in a person, and 150 becomes unbearable for him.

For all living organisms, including humans, sound is one of the environmental influences.

In nature, loud sounds are rare, the noise is relatively weak and short-lived. The combination of sound stimuli gives animals and humans the time necessary to assess their character and formulate a response. Sounds and noises of high power affect the hearing aid, nerve centers, and can cause pain and shock. This is how noise pollution works.

The level of industrial noise is very high. In many jobs and noisy industries it reaches 90-100 decibels or more. It’s not much quieter in our home, where new sources of noise are appearing - the so-called household appliances.

Thus, two types of noise are distinguished:

1. Noises of natural origin.

2. Noises of anthropogenic origin.

2. Changes in the hearing system under the influence of loud sounds

Which organ reacts first to excessive noise? Of course it is an organ of hearing.

The quiet rustling of leaves, the murmur of a stream, bird voices, the light splash of water and the sound of the surf are always pleasant to a person. They calm him down and relieve stress. This is used in medical institutions, in psychological relief rooms. But the natural sounds of nature’s voices are becoming increasingly rare, disappearing completely or are drowned out by industrial, transport and other noises.

Long-term noise adversely affects the hearing organ, reducing sensitivity to sound. It leads to disruption of the heart and liver, and to exhaustion and overstrain of nerve cells. Weakened cells of the nervous system cannot clearly coordinate the work of various body systems. This is where disruptions in their activities arise.

For a long time, the effect of noise on the human body was not specifically studied, although already in ancient times they knew about its harm.

Currently, scientists in many countries around the world are conducting various studies to determine the effect of noise on human health. Their research showed that noise causes significant harm to human health, but absolute silence also frightens and depresses him. Scientists have also found that sounds of a certain strength stimulate the thinking process, especially the counting process.

Each person perceives noise differently. Much depends on age, temperament, health, and environmental conditions.

Some people lose their hearing even after short exposure to relatively low intensity noise.

Constant exposure to loud noise can not only negatively affect your hearing, but also cause other harmful effects - ringing in the ears, dizziness, headaches, and increased fatigue.

Noise has an accumulative effect, that is, acoustic irritations, accumulating in the body, increasingly depress the nervous system. Therefore, before hearing loss from exposure to noise, a functional disorder of the central nervous system occurs. Noise has a particularly harmful effect on the neuropsychological activity of the body.

Noise is insidious, its harmful effects on the body occur invisibly, imperceptibly. Disturbances in the body are not immediately detected. In addition, the human body is practically defenseless against noise.

Table. Sound volume levels from different sources

Sound Source Level (dB)

Quiet breathing is not perceived

Rustle of leaves in calm weather 17

Flipping through newspapers 20

Normal noise in the house 40

Surf on the shore 40

Medium volume conversation 50

Loud talking 70

Working vacuum cleaner 80

Train in metro 80

Rock music concert 100

Roll of Thunder 110

Jet engine 110

Shot from gun 120

Pain threshold 120

Practical part

1. Determination of hearing acuity in students

Hearing acuity is the minimum sound volume that can be perceived by the subject's ear.

In order to determine the hearing acuity of students, we took a mechanical watch and a ruler.

Equipment:

Mechanical watch Ruler

Operating procedure:

1. Bring the watch closer to you until you hear a sound. Measure the distance from your ear to the watch in centimeters.

2. Place the watch tightly against your ear and move it away from you until the sound disappears. Determine the distance to the clock again

3. If the data matches, this will be approximately the correct distance.

4. If the data does not match, then to estimate the hearing distance you need to take the arithmetic mean of the two measurements.

50 students participated in the experiment, including:

1. lovers of listening to loud music on headphones;

2. calm music;

3. lovers of silence

Evaluation of test results:

1. lovers of listening to loud music with headphones - 8-9 cm;

2. calm music - 12-13cm;

3. lovers of silence - 15-16 cm.

■ With constant stretching of the eardrum, its elasticity decreases, so a high volume of sound is required for it to begin to vibrate, that is, the sensitivity of the auditory analyzer decreases;

■ Auditory receptors are damaged.

Sociological survey to identify the effect of noise on the mental processes of 8th grade students

How does noise affect you?

■ Fatigue;

■ Memory loss;

■ Decreased attention;

■ Loss of performance;

■ Sleep disturbance;

■ General weakness

Impact of noise on teachers

(20 people)

How does noise affect you?

■ Annoyance;

■ Decreased functional activity;

■ Difficulties in the family;

■ Loss of performance;

■ Increased irritability;

■ Loss of sleep;

Conclusions: long-term noise leads to rapid fatigue, weakened memory, decreased attention, loss of performance, increased irritability, sleep disturbance, and general weakness. Exposure to noise can gradually lead to mental illness.

Impact of noise leading to mental illness

Effect of noise

Difficulties of mutual understanding

Dissipation of attention

Poor concentration

Losing sleep

Irritability

Decreased functional activity

Discontent

Difficulties in the family

Mental illness

Conclusion

Measures to protect people from noise exposure.

So noise is harmful. “Noise is a slow killer,” say American experts. But is it possible to reduce its impact on living organisms, including humans? What can each of us do?

Like all other types of anthropogenic impacts, the problem of noise pollution is international in nature. The World Health Organization, taking into account the global nature of environmental noise pollution, has developed a long-term program to reduce noise in cities and towns around the world.

In Russia, protection from noise exposure is regulated by the Law of the Russian Federation “On Environmental Protection” (2002) (Article 55), as well as government regulations on measures to reduce noise at industrial enterprises, in cities and other populated areas.

Protection from noise exposure is a very complex problem and its solution requires a set of measures: legislative, technical and technological, urban planning, architectural and planning, organizational, etc. To protect the population from the harmful effects of noise, regulatory legislative acts regulate its intensity, duration of action and other parameters. Gosstandart established uniform sanitary and hygienic standards and rules for limiting noise in enterprises, cities and other populated areas. The standards are based on such levels of noise exposure, the effect of which over a long period of time does not cause adverse changes in the human body, namely: 40 dB during the day and 30 at night. Permissible levels of transport noise are set within 84-92 dB and will decrease over time.

Technical and technological measures come down to noise protection, which is understood as comprehensive technical measures to reduce noise in production (installation of soundproofing casings of machines, sound absorption, etc.), in transport (emission mufflers, replacement of shoe brakes with disc brakes, sound-absorbing asphalt, etc.).

At the urban planning level, protection from noise pollution can be achieved by the following measures:

Zoning with removal of noise sources outside the building;

Organization of a transport network that excludes the passage of noisy highways through residential areas;

Removing noise sources and creating protective zones around and along noise sources and organizing green spaces;

Laying highways in tunnels, constructing noise-protective embankments and other noise-absorbing obstacles along the paths of noise propagation (screens, excavations, forging holes);

Architectural and planning measures provide for the creation of noise-protective buildings, i.e., buildings that provide the premises with normal acoustic conditions with the help of structural, engineering and other measures (sealing windows, double doors with a vestibule, cladding walls with sound-absorbing materials, etc.).

A certain contribution to protecting the environment from noise impacts is made by the prohibition of sound signals from vehicles, flights over the city, restriction (or prohibition) of aircraft takeoffs and landings at night, and other organizational measures.

However, these measures are unlikely to give the desired environmental effect if the main thing is not understood: protection from noise exposure is not only a technical problem, but also a social one. It is necessary to cultivate a sound culture and consciously prevent actions that would contribute to an increase in noise pollution in the environment.

NOISE AS AN ECOLOGICAL FACTOR

Goal of the work: familiarization with the characteristics of noise and the features of its impact on the human body, with the features of measuring and normalizing noise parameters, as well as with methods for assessing noise in natural environmental conditions.

Theoretical part

1. Sound and its main characteristics

Any violation of the stationary state of a particular medium gives rise to wave processes. Mechanical vibrations of medium particles in the frequency range 20 – 20000 Hz are perceived by the human ear and are called sound waves. Fluctuations of the environment with frequencies below 20 Hz called infrasound, and vibrations with frequencies above 20,000 Hz– ultrasound. Sound wavelength l related to frequency f and the speed of sound with the dependence: l =c/f . The unsteady state of the medium during the propagation of a sound wave is characterized by sound pressure ( P ), which is understood as the root-mean-square value of the deviation of pressure in a medium during the propagation of a sound wave from pressure in an undisturbed medium, measured in pascals ( Pa The transfer of energy by a plane sound wave through a unit surface perpendicular to the direction of propagation of the sound wave is characterized by sound intensity (sound power flux density), W/m2: , (1)

Where P – sound pressure, Pa; r – specific density of the medium, g/m 3; c – the speed of propagation of a sound wave in a given medium, m/s. The speed of energy transfer is equal to the speed of propagation of the sound wave.

The human hearing organs are capable of perceiving sound vibrations in very wide ranges of changes in intensities and sound pressures. For example, with a sound frequency of 1 kHz The average sensitivity threshold of the human ear (hearing threshold) corresponds to the values ​​of sound pressure and sound intensity: P0 = 2∙10 -5 Pa And I 0 = 10 -12 W/m2, and the pain threshold (exceeding which can lead to physical damage to the hearing organs) corresponds to the values P b = 20 Pa And I b = 1 W/m2. Quantities P0 And I 0 in sound engineering they are accepted as standard (reference) quantities. According to the Weber-Fechner law, the irritating effect of sound on the human ear is proportional to the logarithm of sound pressure, therefore in practice, instead of absolute values ​​of intensity and sound pressure, their relative logarithmic sound levels, expressed in decibels, are usually used ( dB): ; , (2)

Where I 0 = 10 -12 W/m2 And P 0 = 2∙10 -5 Pa– standard threshold values ​​for intensity and sound pressure. For real atmospheric conditions we can assume that L I = L P = L .

The real noise field is often determined not by one, but by several noise sources. The experimentally established rule for adding the sound intensities of several sources looks the simplest: . (3) The rule for adding sound pressures created by several sources is easily derived from expressions (1), (3) and is quadratic in nature:

Using expressions (2) – (4), it is easy to obtain the rule for adding relative logarithmic sound levels. According to the definition, relative logarithmic sound levels i th source and the total sound level are determined as

whence we get accordingly:

. (5) The total sound level can be expressed similarly: .Substituting expressions (5) and (4) here in sequence, we obtain the rule for adding the relative logarithmic sound levels of several sources: . (6) In the case of n identical sound sources (Li = L), formula (6) is simplified: L å = L + 10 lg ( n ) . (7) From formulas (6) and (7) it follows that if the level of one of the sound sources exceeds the level of the other by more than 10 dB, then the sound of the weaker source can practically be neglected, since its contribution to the overall level will be less than 0, 5 dB. Thus, when dealing with noise, it is first necessary to drown out the most intense sources of noise. In addition, it should be borne in mind that if there are several identical noise sources, eliminating one or two of them has very little effect on the overall reduction in noise level. An important characteristic of a noise source is its sound power level. Sound power W , W, is the total amount of sound energy emitted by a noise source per unit time. . (8) If energy is radiated uniformly in all directions and the attenuation of sound in the air is small, then at intensity I on distance r from a noise source, its sound power can be determined by the formula: W=4 p r2I . By analogy with logarithmic levels of intensity and sound pressure, logarithmic levels of sound power ( dB): , (9)

Where W 0 = I 0 s 0 = 10 -12 – standard sound power value, W; s 0 = 1 m 2.

The distribution of noise energy in the audio frequency range is characterized using the frequency spectrum. In practical applications, the noise spectrum shows sound pressure or intensity levels (for sound sources, sound power levels) in octave frequency bands characterized by lower f n and top f in boundary frequencies in the ratio f in / f n = 2 and geometric mean frequency: f сг = (f n · f in) 0.5 . The geometric mean frequencies of adjacent octave bands correspond to a standard binary series, including 10 values: 31.5; 63; 125; 250; 500; 1000; 2000; 4000; 8000; 16000 Hz.

2. Features of subjective perception of sound

The perception of sound by the human ear depends very strongly and nonlinearly on its frequency. Features of subjective perception of sound are illustrated graphically using curves of equal loudness in Fig. 1. Each curve in Fig. 1 characterizes the sound pressure levels at various frequencies perceived by the human ear with the same volume level ( L N ).

Rice. 1. Equal Loudness Curves

The relative logarithmic loudness level is estimated using special units - background. To determine the volume level of an arbitrary point N in the drawing field in Fig. 1, draw an equal loudness curve through this point (as shown by the dotted line in Fig. 1) and determine the sound pressure level ( L P * ) at which this curve crosses the frequency line at 1000 Hz. The numerical value of the sound pressure level obtained in this way, expressed in dB, and will determine the numerical value of the volume level, expressed in background, i.e.: .Physical device for measuring sound pressure levels (an objective physical parameter) – “ sound level meter» – technically easy to implement. To assess loudness levels (a parameter subjectively perceived by a person), it is necessary, as follows from the drawing in Fig. 1, adjust the measuring process in the sound level meter so that when the sound pressure level changes in accordance with one of the equal loudness curves, its readings remain unchanged and equal to the sound pressure level at a frequency of 1000 Hz. That is, for an arbitrary curve of equal loudness (for example, shown by the dotted line in Fig. 1), it is necessary that the following condition be met: It is not possible to carry out precise correction using relatively simple technical means. Therefore, practically feasible correction is carried out approximately. Several types of correction of sound level meter readings are possible to estimate loudness levels. The most widely used correction is called type correction A . Thus, corrected sound pressure levels obtained using a physical sound level meter (i.e. operating in type correction mode) A ) and taken as estimates of loudness levels subjectively perceived by a person, are defined as (10)

and are called sound levels, measured in special units dBA.

From the above, we can draw the following conclusion: if any of the curves of equal loudness for a tonal sound is subjected to correction A , then as a result we obtain the value of a constant sound level (in dBA), approximately (exact correction is practically impossible) corresponding to the volume level ΔL N given curve, expressed in loudness units ( background), i.e. you can read the sound levels L A an approximate estimate of the subjective perception of noise in the form of loudness levels L N : .

3. The effect of noise on the human body

Noise Any sound that has an adverse effect on the human body is considered. Depending on the intensity and duration of the effect of noise on the human body, a decrease in the sensitivity of the hearing organs occurs, expressed in the form of a temporary shift in the hearing threshold (lower curve in Fig. 1). As a result of this shift in the sensitivity threshold of the hearing aid, a person begins to have trouble hearing quiet sounds. As a rule, the sensitivity threshold is restored after a certain (relatively short) time interval. However, with high intensity and duration of exposure to noise, an irreversible loss of sensitivity of the human hearing aid (hearing loss) is possible. Regular long-term exposure of a person to intense noise (with a level exceeding 80 dBA) usually sooner or later leads to partial or even complete hearing loss. Research shows that hearing loss is currently one of the leading occupational diseases and has a tendency to further increase. The effect of noise on the body is not limited to just the direct effect on the hearing organs. Sound stimulation through the nervous system of the auditory organs is transmitted to the central and autonomic nervous systems and through them can affect the internal organs of a person, causing significant changes in their condition. Thus, noise can have an impact on the human body as a whole. This fact is confirmed by the fact that the statistics of the general morbidity of workers in noisy industries is 10 - 15% higher. The impact on the autonomic nervous system is manifested even at low sound levels (40 - 70 dBA) and does not depend on the subjective perception of noise by a person. Of the autonomic reactions, the most pronounced are impaired peripheral circulation as a result of narrowing of the capillaries of the skin and mucous membranes, as well as increased blood pressure (at sound levels above 85 dBA). The impact on the human central nervous system causes an increase in the time of visual-motor reactions, disrupts the bioelectrical activity of the brain with the possible occurrence of general functional changes in the body (at sound levels above 50 - 60 dBA), and also biochemical changes occur in the structures of the brain. Noise can have a mental impact on a person, starting from sound levels of 30 dBA. The impact on the human psyche increases with increasing sound intensity, as well as with decreasing bandwidth of the frequency spectrum of the noise. With pulsed and irregular noise, the degree of their impact increases. Changes in the states of the central and autonomic nervous systems occur much earlier and at lower noise levels. Symptoms of “noise disease” include: decreased hearing sensitivity, changes in digestive functions (low acidity), cardiovascular failure, neuroendocrine disorders. Under the influence of noise, attention and memory levels decrease, increased fatigue occurs, and headaches may occur.

4. Noise regulation

Based on the nature of the spectrum, noise is divided into broadband and tonal. Broadband noise has a continuous frequency spectrum less than one octave wide. The tonal noise spectrum contains pronounced discrete tones, determined by measurements in one-third octave frequency bands with the sound pressure level exceeding the neighboring bands by at least 10 dB.According to time characteristics, noise is divided into constant noise, the sound level of which during an 8-hour working day changes by no more than 5 dBA when measuring on the time characteristic of a “slow” sound level meter, and non-constant noise that does not satisfy this condition. Non-constant noise, in turn, is divided into the following types:

• time-varying noises, the sound level of which continuously changes over time;
• intermittent noises, the sound level of which changes stepwise (by 5 dBA and more), and the duration of the intervals during which the level remains constant is at least 1 With;
• impulse noise, consisting of one or more sound signals, each lasting less than 1 With, while sound levels in dBA And dBA(I) , measured respectively on the time characteristics “ slowly" And " pulse” sound level meter, differ by at least 7 dBA.

To assess non-constant noise, the concept of equivalent sound level LAe (in terms of impact energy), expressed in dBA and representing the sound level of such constant broadband noise, the intensity of which during the considered time interval ( T ) has the same average value as the given time-varying noise: ,

Where L A ( t ) – current values, respectively, of sound pressure and sound level of time-varying noise. Values L A uh can be measured using automatic integrating sound level meters over a specified period T.

The normalized noise parameters are: for constant noise– sound pressure levels L P (dB) in octave frequency bands with geometric mean frequencies of 31.5; 63; 125; 250; 500; 1000; 2000; 4000 and 8000 Hz; In addition, for an approximate assessment of constant broadband noise in workplaces, it is permissible to use the sound level L A , expressed in dBA;For intermittent noise(except pulse) – equivalent sound level L Ae (by impact energy), expressed in dBA, represents the sound level of such a constant broadband noise that affects the ear with the same sound energy as real, time-varying noise over the same period of time; for impulse noise– equivalent sound level L Ae , expressed in dBA, and maximum sound level L A max V dBA(I), measured on the time characteristic of the “impulse” of the sound level meter. Permissible values ​​of noise parameters at workplaces are regulated by GOST 12.1.003-83* “Noise. General safety requirements” and SN 3223-85 “Sanitary standards for permissible noise levels in workplaces”. Permissible values ​​of noise parameters are established depending on the type of work performed (workplaces) and the nature of the noise. For work related to creative, managerial, scientific activities or requiring increased attention, concentration, auditory control, lower noise levels are provided. Below are the characteristic types of work distinguished during standardization, indicating the serial number. Creative, scientific work, training, design , design, development, programming. Administrative and managerial work that requires concentration, analytical work in the laboratory. Dispatcher work that requires voice communication by telephone, in computer information processing rooms, in precision assembly areas, in typing offices. Work in premises for placement of noisy computer units associated with monitoring and remote control processes without voice communication by telephone; work in laboratories with noisy equipment. All types of work except those listed in paragraphs. 1 – 4. For broadband noise in table. 1 shows permissible sound pressure levels L P in octave frequency bands with geometric mean frequencies f сг , sound levels L A (for a subjective assessment of the volume of constant noise) and equivalent sound levels L Ae (to assess intermittent noise). For tonal and impulse noise, as well as for noise generated indoors by air conditioning and ventilation installations, the permissible levels should be 5 dB below those indicated in Table 1 (when measured on the “slow” characteristic of the sound level meter).

Table 1

Acceptable noise levels

type of work	Sound pressure levels L P (dB) in octave frequency bands with geometric mean frequencies, Hz									Sound levels L A , dBA

For time-varying and intermittent noise, the maximum sound level should not exceed 110 dBA.For impulse noise, the maximum sound level measured on the “impulse” characteristic of the sound level meter should not exceed 125 dBA(I).According to SN 3077-84, more stringent noise requirements are established in residential premises, public buildings and in residential areas. For example, in the classrooms of educational institutions the levels L A And L Ae should not exceed 40 dBA, and the maximum sound level is 55 dBA.In any case, even short-term stay of people in areas with sound pressure levels above 135 is prohibited dB in any octave band. Zones with sound level above 85 dB must be marked with safety signs; Workers in such areas should be provided with personal protective equipment.

5. Features of sound propagation in the atmosphere

Sound level ( dB) created by a point source at a distance r (m) from it in a homogeneous environment without absorption and far from any obstacles, is determined by the formula: , (11)

Where L W – relative logarithmic level of sound power of the source (formula (9)); f – directivity factor of sound emission from the source relative to the control point (for point sound sources considered in this work, f= 1); Ω – solid (spatial) angle of sound radiation from the source, Wed; Δ L V – additional attenuation of the sound level caused by the absorption of sound wave energy by atmospheric air.

The sound pressure level created by a sound source at an observation point some distance from the source depends on the characteristics of the source (emitted spectrum, radiation directivity characteristics), on the location of the observation point (control point) relative to the sound source and a number of other parameters. Solid angle ( W ) is a part of space limited by a conical surface. A conical surface in the general case is a set of straight lines (generators) in three-dimensional space connecting all points of a certain line (guide) with a given point (vertex). The measure of a solid angle is the ratio of the area of ​​that part of the surface of a sphere s arbitrary radius r with the center at the vertex of the solid angle, which is cut by the conical surface of the given solid angle, to the square of the radius of the sphere (Fig. 2): , steradian (Wed). (12) A conical surface is represented as a set of straight lines ( forming) in space connecting all points of some, in general arbitrary, line ( guide) with a given point ( top), as shown in Fig. 2.

If the sound source is located in free space and radiates in all directions (not necessarily equally), then the solid angle of radiation will be equal to the full solid angle (the solid angle encloses the entire space): W = 4 p Wed.

When the sound source is located on a certain plane, for example on the earth's surface, the solid angle will include a half-space and, therefore, the value of the solid angle in this case will be 2 p Wed.From expression (11), without taking into account the value Δ L in , it follows that the sound pressure level at the control point decreases by 6 dB when the distance to the sound source doubles. This decrease in sound pressure is called “geometric sound level decay.” In the real environment, the vast majority of sound sources are located near the earth’s surface, which has a certain sound reflectivity. In such cases, the sound level at the control point will be determined by both direct and reflected sound waves (Fig. 3). In Fig. 3 is indicated: r 1 And r 2 – distances traveled by direct and reflected sound waves, m; h sh And h k.t. – the height of the location of the sound source and the control point above the surface. Taking into account the designations in Fig. 3 there is a formula for estimating the level of sound propagating near a reflective surface: , (13)where: f 1 And f 2 – factors of directionality of sound emission from the source in the direction of the control point and in the direction of the point of reflection of the sound wave from the surface (in this work, for point noise sources, they are taken equal to 1); a negative – coefficient of reflection of the sound wave from the surface (0< a negative < 1, для земной поверхности a negative = 0.37).At h sh £ r 1 / 3 And a op ≈ 1, with a slight error, we can assume that sound emission occurs directly from the surface. In this case it is believed r 1 ≈ r 2 ≈ r (Fig. 4), f = 0,5(f 1 + f 2)= 1 and W= 2p Wed(radiation of sound into a half-space) and formula (11) is used as the calculation formula. If h k.t << r , h sh << r And f avg £ 40/ (h sh h k.t. ) – average frequency of the frequency band emitted by the source, Hz, then the direct and reflected sound waves add up in phase and the sound pressure level increases by D L extra = 3 dB relative to the level determined by formula (14). Additional attenuation of the sound level caused by losses of sound energy in the atmospheric air is proportional to the distance r (m), passed by the sound wave: , (14)

Where b V – sound absorption coefficient in air, dB/km. Magnitude b V depends on the sound frequency, as well as on the temperature and relative humidity of the air (in this work it is accepted b V =5,2 dB/km).

Additional noise attenuation along the path of sound waves in the environment can be caused by various obstacles, such as forest belts. If the height of forest plantations is at least 5 m, then the sound is partially reflected from it, and partially scattered in the crowns of trees and bushes. Additional noise attenuation by a forest belt can be taken into account by calculating a negative correction to formulas (11) and (13): D L l.p. = b l.p. b l.p , (15)where: b l.p. – coefficient of sound attenuation by a strip of forest plantations, dB/m; b l.p – width of the forest belt, m. The sound attenuation coefficient of a forest belt depends in a complex way on the type of vegetation and the type of planting, as well as on its width. The average value of the sound attenuation coefficient of a forest belt is considered to be b l.p. = 0,08 dB/m. It should, of course, be borne in mind that a forest belt consisting of deciduous plantations in winter practically does not weaken the level of the sound wave passing through it. The above formulas allow you to estimate the noise level at some distance from its point source. However, there are noise sources in the environment, such as long streets, highways, noisy production workshops, etc., which cannot be considered point sources. Such noise sources are called extended or linear. Sound pressure level ( dB) when moving away to a distance d from an infinitely long linear noise source in a medium without absorption is reduced by 3 dB when the distance is doubled ( d , m) : L k.t. = L* W – 10 lg( d) – 3 , (16)where L * W – relative logarithmic level of sound power emitted by a section of an extended source of length 1 m. Sound pressure levels created by individual sections of linear sources or extended sources of finite length at an arbitrarily located control point (Fig. 4) are determined by the formula: . (17) In Fig. 4 is indicated: l – length of an extended noise source, m; d – the shortest distance from the front of an extended noise source to the control point, m; α – the angle at which an extended noise source is visible from a given control point, glad; r – distance from the middle of an extended noise source to the control point, m. If r > 2l w , then we can use formula (14) with f = 1 and Ω = 2p Wed, i.e., an extended source in this case can be considered a point source.

Rice. 4. To determine the sound pressure level near an extended noise source of finite length

At a sufficiently large distance from an extended noise source, corrections should be made in formulas (16) and (17) for sound absorption by the air (formula (14)) and, if necessary, for noise attenuation by a forest shelterbelt (formula (14)).

Practical part

1. Get a version of the assignment from the teacher.

2. Study the assignment received.

3. Classify the noise in a given situation.

4. Using appropriate calculations, estimate the noise level in situations determined by the task option.

5. Based on the calculation results, construct the graphical dependencies specified in the task.

6. Evaluate the obtained noise characteristics for compliance with standard levels.

1) The report must contain the results of the required calculations and graphical dependencies illustrating the results of the calculations.

2) Based on the task data, classify the noises under study (determine their nature).

3) Give a conclusion on the compliance of the calculated noise levels at given control points with standard levels.

Control questions

1. Sound and its characteristics.
2. Features of subjective perception of sound by the human hearing organs.
3. The effect of noise on the human body.
4. Characteristics of noise and their classification.
5. For what purpose was the idea of ​​equivalent sound level introduced and what does this parameter represent?
6. Principles of noise regulation.
7. Peculiarities of perception of noise coming from several sources.
8. An idea of ​​the solid angle within which sound emission occurs.
9. What factors can influence the level of perceived sound as it propagates in atmospheric air.
10. Features and differences between point and extended sound sources.
11. Fighting noise at work: Directory / Ed. ed. E. Ya. Yudina. M.: Mashinostroenie, 1985. pp. 11 – 17, 36 – 57.
12. Environmental protection / Ed. S. V. Belova. M.: Higher School, 1991. P. 200 – 234.
13. Denisenko G.F. Occupational Safety and Health. M.: Higher School, 1985. pp. 182 – 193.

Bibliography

Laboratory work No. 4

DETERMINATION OF CONDITIONS FOR DISPERSION OF EMISSIONS BY INDUSTRIAL ENTERPRISES

Goal of the work: determine the level of atmospheric air pollution from industrial emissions and emissions from ventilation devices.

Theoretical part

1. Technogenic emissions and environmental impacts

Technogenic pollution of the environment is the most obvious causal relationship in the ecosphere system: “economy, production, technology, environment.” It leads to degradation of ecological systems, global climatic and geochemical changes, and damage to people and animals. Figure 1 shows the classification of man-made environmental pollution.

Rice. 1. Classification of man-made environmental pollution

In general, in terms of nature and scale, chemical pollution is the most significant, and the greatest threat is associated with radiation. As for the objects of influence, in the first place, of course, is the person. Recently, not only the growth of pollution, but also their total impact, which often exceeds the final effect of a simple summation of the consequences, has been particularly dangerous. From an environmental point of view, all products of the technosphere are pollution or potential pollutants, even those that are chemically inert, since they take up space in the biosphere and become ballast of environmental flows. Most industrial products also become pollutants over time, representing “deposited waste.” Most environmental pollution relates to unintentional, although obvious, environmental violations. Many of them are significant, many are difficult to control and they are dangerous due to unforeseen effects due to the remoteness of the consequences. For example: man-made emissions of CO 2 or thermal pollution are fundamentally inevitable as long as fuel energy exists. The scale of waste of modern humanity and products of the technosphere is almost 160 Gt/year, of which about 10 Gt form a mass of products, i.e. "delayed departure". On average, there are about 26 T of all anthropogenic emissions per year. 160 Gt waste is distributed approximately as follows: 30% is released into the atmosphere, 10% ends up in water bodies, 60% remains on the surface of the Earth. The chemicalization of the biosphere has now reached a very large scale, which significantly affects the geochemical appearance of the ecosphere. The total mass of produced chemicals and active waste from the entire chemical industry of the world exceeded 1.5 Gt/year. Almost all of this amount can be attributed to OS pollution. But it’s not just the mass, but also the variety and toxicity of most of the chemicals produced. There are more than 10 7 chemical compounds in the world chemical nomenclature, and their number increases by several thousand every year. However, most of the substances used have not been assessed in terms of their toxicity and environmental hazard.

2. Sources of technogenic emissions

All sources of man-made emissions are divided into organized, stationary and mobile. Organized sources are equipped with special devices for directed emission removal (pipes, ventilation shafts, outlet channels, gutters, etc.). Emissions from fugitive sources are arbitrary. Sources are also divided by geometric characteristics (point, linear, derivative) and by operating mode - continuous, periodic, burst. The sources of the predominant part of chemical and thermal pollution are thermochemical processes in the energy sector - fuel combustion and associated thermal and chemical processes and leaks. The main reactions that determine the emission of carbon dioxide, water vapor and heat proceed as follows:

Carbon: C + O 2 → CO 2;

Hydrocarbons: C n H m + (n + 0.25m)O 2 → nCO 2 + 0.5mH 2 O .

Along the way, reactions occur that determine the emission of other pollutants, and they are associated with the content of various impurities in the fuel, with the thermal oxidation of air nitrogen and with secondary reactions occurring in the OS. All these reactions accompany the operation of thermal stations, industrial furnaces, internal combustion engines, gas turbine and jet engines, processes in metallurgy, roasting of mineral raw materials, etc. The greatest contribution to energy-dependent environmental pollution is made by thermal power engineering and transport. The general picture of the impact of a thermal power plant (CHP) on the environment is shown in Fig. 2. When fuel is burned, its entire mass turns into solid, liquid and gaseous waste. Data on emissions of the main air pollutants during the operation of thermal power plants are given in table. 1.

Table 1

Specific emissions into the atmosphere during the operation of thermal power plants with a capacity of 1000 MW on different types of fuel, g/kW hour

			Natural gas

The amount of emissions depends on the quality of the fuel, the type of combustion units, emission neutralization systems and dust collectors and wastewater treatment devices. On average, in the fuel thermal power industry, by 1 T of burned fuel is emitted into the OS about 150 kg pollutants.

Rice. 2. Impact of thermal power plant on the environment

1 – boiler; 2 – pipe; 3 – steam pipe; 4 – electric generator; 5 – electrical substation; 6 – capacitor; 7 – water intake for cooling the condenser; 8 – water supply to the boiler; 9 – power lines; 10 – electricity consumers; 11 - pond

Metallurgical processes are based on the recovery of metals from ores, where they are contained primarily in the form of oxides or sulfides, using thermal and electrolytic reactions. The most typical summary (simplified) reactions:

iron: Fe 2 O 3 + 3C + O 2 → 2Fe + CO + 2CO 2;

copper: Cu 2 S + O 2 → 2Cu + SO 2;

aluminum (electrolysis): Al 2 O 3 + 2O → 2Al + CO + CO 2.

The technological chain in ferrous metallurgy includes the production of pellets and agglomerates, coke, blast furnace, steelmaking, rolling, ferroalloy, foundry and other auxiliary technologies. All metallurgical processes are accompanied by intense environmental pollution (Table 2). In coke production, aromatic hydrocarbons, phenols, ammonia, cyanides and a number of other substances are additionally released. Ferrous metallurgy consumes large amounts of water. Although industrial needs are 80–90% satisfied through recycling water supply systems, the intake of fresh water and the discharge of contaminated wastewater reach very large volumes, respectively about 25–30 m 3 and 10 – 15 m 3 by 1 T full cycle products. Significant amounts of suspended substances, sulfates, chlorides, and heavy metal compounds enter water bodies with wastewater.

table 2

Gas emissions (before cleaning) from the main stages of ferrous metallurgy

(without coke production), in kg/t corresponding product

	Production
	Sintering	Domain	Steelmaking	Rental

* kg/m 2 metal surface

Non-ferrous metallurgy, despite the relatively smaller material flows of production, is not inferior to ferrous metallurgy in terms of total toxicity of emissions. In addition to a large amount of solid and liquid waste containing such dangerous pollutants as lead, mercury, vanadium, copper, chromium, cadmium, thallium, etc., many air pollutants are also released. During metallurgical processing of sulfide ores and concentrates, a large mass of sulfur dioxide is formed. Thus, about 95% of all harmful gas emissions from the Norilsk Mining and Metallurgical Plant account for SO 2, and the degree of its utilization exceeds 8%. Technologies of the chemical industry with all its branches (basic inorganic chemistry, petrochemical chemistry, forest chemistry, organic synthesis, pharmacological chemistry, microbiological industry, etc.) contain many essentially open material cycles. The main sources of harmful emissions are the production processes of inorganic acids and alkalis, synthetic rubber, mineral fertilizers, pesticides, plastics, dyes, solvents, detergents, and oil cracking. The list of solid, liquid and gaseous waste from the chemical industry is huge both in terms of the mass of pollutants and their toxicity. In the chemical complex of the Russian Federation, more than 10 million tons hazardous industrial waste. Various technologies in manufacturing industries, primarily in mechanical engineering, include a large number of different thermal, chemical and mechanical processes (foundry, forging, machining, welding and cutting of metals, assembly, galvanic, paint and varnish processing, etc. .). They produce a large volume of harmful emissions that pollute the environment. A noticeable contribution to the overall environmental pollution is also made by various processes accompanying the extraction and enrichment of mineral raw materials and construction. Agriculture and the everyday life of people using their own waste - the remains and waste products of plants, animals and humans - are essentially not sources of environmental pollution, since these products can be included in the biotic cycle. But, firstly, modern agricultural technologies and municipal services are characterized by concentrated discharge of most waste, which leads to significant local excesses of permissible concentrations of organic matter and phenomena such as eutrophication and contamination of water bodies. Secondly, and even more seriously, agriculture and people’s everyday life are intermediaries and participants in the dispersal and distribution of a significant part of industrial pollution in the form of distributed flows of emissions, residues of petroleum products, fertilizers, pesticides and various used products, garbage - from toilet paper to abandoned farms and cities.

Rice. 3. Scheme of the effects of environmental pollution

Between all environments there is a constant exchange of part of the pollutants: the heavy part of aerosols, gas, smoke and dust impurities from the atmosphere falls onto the earth's surface and into water bodies, part of the solid waste from the earth's surface is washed into water bodies or dispersed by air currents. Environmental pollution affects humans directly or through a biological link (Fig. 3). In technogenic flows of pollutants, the key place is occupied by transporting media – air and water.

3. Air pollution

Composition, quantity and danger of air pollutants. Out of 52 Gt More than 90% of global anthropogenic emissions into the atmosphere come from carbon dioxide and water vapor, which are not usually classified as pollutants (the special role of CO 2 emissions is discussed below). Man-made emissions into the air number tens of thousands of individual substances. However, the most common, “high-tonnage” pollutants are relatively few in number. These are various solid particles (dust, smoke, soot), carbon monoxide (CO), sulfur dioxide (SO 2), nitrogen oxides (NO and NO 2), various volatile hydrocarbons (CH x), phosphorus compounds, hydrogen sulfide (H 2 S ), ammonia (NH 3), chlorine (Cl), hydrogen fluoride (HF). The quantities of the first five groups of substances from this list, measured in tens of millions of tons and emitted into the air around the world and Russia, are presented in Table. 3.

Table 3

Air emissions of the five main pollutants in the world and in Russia ( million tons)

	Stationary sources	Transport	Stationary sources		Transport

The greatest air pollution is observed in industrial regions. About 90% of emissions come from 10% of the land area and are concentrated mainly in North America, Europe and East Asia. The air basin of large industrial cities is especially heavily polluted, where man-made heat flows and aeropollutants, often under unfavorable weather conditions (high atmospheric pressure and thermal inversions), often create dust domes and smog phenomena - toxic mixtures of fog, smoke, hydrocarbons and harmful oxides. Such situations are accompanied by strong excesses of the maximum permissible concentrations of many air pollutants. More than 200 cities in Russia, with a population of 65 million people experience constant excesses of the maximum permissible concentrations of toxic substances. Residents of 70 cities systematically encounter MPC exceedances of 10 times or more. Among them are cities such as Moscow, St. Petersburg, Samara, Yekaterinburg, Chelyabinsk, Novosibirsk, Omsk, Kemerovo, Khabarovsk. In the listed cities, the main contribution to the total volume of emissions of harmful substances comes from motor vehicles, for example, in Moscow it is 88%, in St. Petersburg - 71%. The earth's atmosphere has the ability to self-purify itself from pollutants, thanks to the physical and chemical processes occurring in it. and biological processes. However, the power of technogenic sources of pollution has increased so much that in the lower layer of the troposphere, along with a local increase in the concentration of some gases and aerosols, global changes are occurring. Man invades the cycle of substances balanced by biota, sharply increasing the emission of harmful substances into the atmosphere, but not ensuring their removal. The concentration of a number of anthropogenic substances in the atmosphere (carbon dioxide, methane, nitrogen oxides, etc.) is growing rapidly. This indicates that the assimilation potential of the biota is close to exhaustion. Acid precipitation. Based on a number of indicators, primarily in terms of the mass and prevalence of harmful effects, sulfur dioxide is considered the number one atmospheric pollutant. It is formed by the oxidation of sulfur contained in fuel or in sulfide ores. Due to the increase in the power of high-temperature processes, the conversion of many thermal power plants to gas and the growth of the car fleet, emissions of nitrogen oxides formed during the oxidation of atmospheric nitrogen are increasing. The entry of large quantities of SO and nitrogen oxides into the atmosphere leads to a noticeable decrease in the pH of atmospheric precipitation. This occurs due to secondary reactions in the atmosphere, leading to the formation of strong acids - sulfuric and nitric. These reactions involve oxygen and water vapor, as well as technogenic dust particles as catalysts: 2SO 2 + O 2 + 2H 2 O → 2H 2 SO 4 ; 4NO 2 + O 2 + 2H 2 O → 4HNO 3. In the atmosphere it turns out and a number of intermediate products of these reactions. The dissolution of acids in atmospheric moisture leads to “acid rain”. Acid precipitation is very dangerous in areas with acidic soils; microflora dies, organic matter is washed out, water bodies of rivers and lakes become acidified, and irreversible changes occur in ecosystems. Violation of the ozone layer. In the 1970s, reports emerged of regional declines in stratospheric ozone. The seasonally pulsating ozone hole over Antarctica with an area of ​​more than 10 million km 2, where the O 3 content decreased by almost 50% during the 1980s. Later, “wandering ozone holes,” although smaller in size and not with such a significant decrease, began to be observed in winter in the Northern Hemisphere, in zones of persistent anticyclones - over Greenland, Northern Canada and Yakutia. The average rate of global decline for the period from 1980 to 1995 is estimated at 0.5 - 0.7% per year. Since the weakening of the ozone layer is extremely dangerous for all terrestrial biota and for human health, these data attracted the close attention of scientists, and then the whole society. A number of hypotheses have been put forward about the causes of damage to the ozone layer. Most experts are inclined to believe that ozone holes are of man-made origin. The most substantiated idea is that the main reason is the entry into the upper layers of the atmosphere of technogenic chlorine and fluorine, as well as other atoms and radicals that can extremely actively add atomic oxygen, thereby competing with the reaction O + O 2 → O 3. The introduction of active halogens into the upper layers of the atmosphere are mediated by volatile chlorofluorocarbons (CFCs) such as freons (mixed fluorochlorides of methane and ethane, for example freon-12 - dichlorodifluoromethane, CF 2 Cl 2), which, being inert and non-toxic under normal conditions, disintegrate under the influence of short-wave ultraviolet rays in the stratosphere. Having broken free, each chlorine atom is capable of destroying or preventing the formation of many ozone molecules. Chlorofluorocarbons have a number of useful properties that have led to their widespread use in refrigeration units, air conditioners, aerosol cans, fire extinguishers, etc. Since 1950, the volume of world production CFCs increased annually by 7–10% and in the 80s amounted to about 1 million tons. Subsequently, international agreements were adopted
obliging participating countries to reduce the use of CFCs. The United States introduced a ban on the use of CFC aerosols back in 1978. But the expansion of other uses of CFCs has again led to an increase in global production. The transition of industry to new ozone-saving technologies is associated with large financial costs. In recent decades, other, purely technical ways of introducing active ozone destroyers into the stratosphere have emerged: nuclear explosions in the atmosphere, emissions from supersonic aircraft, launches of reusable rockets and spacecraft. It is possible, however, that part of the observed weakening of the Earth’s ozone screen is associated not with man-made emissions, but with secular fluctuations in the aerochemical properties of the atmosphere and independent climate changes. The greenhouse effect and climate change. Technogenic air pollution is to a certain extent related to climate change. We are talking not only about the quite obvious dependence of the mesoclimate of industrial centers and their surroundings on thermal, dust and chemical air pollution, but also about the global climate. Since the end of the 19th century. to date, there has been a tendency for the average temperature of the atmosphere to increase; over the past 50 years it has increased by approximately 0.7 °C. This is by no means small, considering that the gross increase in the internal energy of the atmosphere is very large - about 3000 MJ. It is not associated with an increase in the solar constant and depends only on the properties of the atmosphere itself. The main factor is a decrease in the spectral transparency of the atmosphere for long-wave back radiation from the earth's surface, i.e. strengthening of the greenhouse effect. The greenhouse effect is created by an increase in the concentration of a number of gases - CO 2, CO, CH 4, NO x, CFCs, etc., called greenhouse gases. According to data compiled recently by the International Panel on Climate Change (IPCC), there is a fairly high positive correlation between the concentration of greenhouse gases and deviations in global atmospheric temperature. Currently, a significant part of greenhouse gas emissions is of technogenic origin. The trend of global warming is given great importance. The question of whether it will happen or not is no longer worth it. According to experts from the World Meteorological Service, at current levels of greenhouse gas emissions, the average global temperature in the next century will increase at a rate of 0.25 °C in 10 years. Its growth by the end of the 21st century, according to different scenarios, (depending on the adoption of certain measures) can range from 1.5 to 4 °C. In northern and middle latitudes, warming will have a stronger impact than at the equator. It would seem that such an increase in temperature should not cause much concern. Moreover, possible warming in countries with cold climates, such as Russia, seems almost desirable. In fact, the consequences of climate change can be catastrophic. Global warming will cause a significant redistribution of precipitation on the planet. The level of the World Ocean due to melting ice may increase by 30 - 40 by 2050 cm, and by the end of the century - from 60 to 100 cm. This will create a threat of flooding of large coastal areas. For the territory of Russia, the general trend of climate change is characterized by slight warming, the average annual air temperature from 1891 to 1994. increased by 0.56 °C. During the period of instrumental observations, the last 15 years were the warmest, and the warmest year was 1999. In the last three decades, a tendency towards a decrease in precipitation has also been noticeable. One of the alarming consequences of climate change for Russia may be the destruction of frozen soils. Temperature increase in the permafrost zone by 2–3 °C will lead to a change in the load-bearing properties of soils, which will jeopardize various structures and communications. In addition, the reserves of CO 2 and methane contained in permafrost from thawed soils will begin to enter the atmosphere, exacerbating the greenhouse effect.

4. Determination of conditions for the dispersion of emissions from industrial enterprises

The distribution of industrial emissions from pipes and ventilation devices in the atmosphere obeys the laws of turbulent diffusion. The process of dispersion of emissions is significantly influenced by the state of the atmosphere, the location of enterprises and emission sources, the nature of the terrain, the chemical properties of emitted substances, the height of the source, the diameter of the pipe, etc. The horizontal movement of impurities is determined mainly by the speed and direction of the wind, and the vertical movement by the distribution of temperatures in the atmosphere along the height. The basis of the “Methods for calculating the concentrations of harmful substances in the atmospheric air contained in emissions from enterprises” OND-86 is the condition under which the total concentration of each harmful substances should not exceed the maximum single maximum permissible concentration of this substance in the atmospheric air. Maximum concentration Cm harmful substances (in mg/m 3) near the earth's surface is formed on the axis of the ejection plume at a distance Xmax from the emission source (for a hot gas-air mixture):

A is the atmospheric stratification coefficient, which depends on the temperature gradient and determines the conditions for vertical and horizontal dispersion of emissions (for the center of Russia it takes a value within 140 – 200);

M – mass of substance emitted into the atmosphere per unit time, g/s;

V 1 – volume of emitted gas-air mixture, m 3 /s;

h – pipe height, m;

F – coefficient taking into account the rate of sedimentation of suspended particles of emission in the atmosphere (for gases it is 1, for dust with a cleaning efficiency of more than 90% - 2, from 75% to 90% - 2.5, less than 75% - 3);

Δ T – the difference between the temperature of the emitted gas-air mixture and the temperature of the surrounding atmospheric air, equal to the average temperature of the hottest month at 13 hours;

η – dimensionless coefficient taking into account the influence of terrain;

m – dimensionless coefficient taking into account the conditions for the release of gases from the pipe:

where: f = 10 3 W 0 D/h 3 ΔT;

W 0 = 4 V 1 / π D 2 – average speed of gases leaving the pipe, m/s;

D – pipe diameter, m;

n – dimensionless coefficient depending on the parameter V M , m/s:

At Vm ≤ 0.3 accept n = 3, at Vm > 2 accept n = 1, at 0.3< Vm < 2 принимают n= [(Vm – 0.3)(4,36 – Vm)] 0,5 .

Expected maximum concentration of pollutants (in mg/m 3) when releasing a cold gas-air mixture is determined by the equation:

Distance to the place where the maximum concentration is expected, ( X max ) is defined as follows: ● for gases and fine dust Xmax = dh , Where d – dimensionless quantity depending on the parameter V M :

for cold exhaust

d = 11.4 V M at V M ≤ 2;

d = 16.1 ( V M) 0.5 at V M > 2;

● for coarse dust ( F ≥ 2)

X max = 0.25(5 – F) dh ;

● for a hot gas-air mixture:

d = 4.95V M (1 + 0.28f 1/3) at V M ≤ 2;

d = 7 ( V M) 0.5 (1 + 0.28 f 1/3) at V M > 2.

Concentration of pollutant in the surface layer of the atmosphere at any distance X from a release source other than Xmax , is determined by the formula: C = Cm S 1 ,

Where S 1 – coefficient depending on the value χ = X / Xmax :

● when χ ≤ 1 S 1 = 3 χ 4 – 8 χ 3 + 6 χ 2 ;

● at 1< χ ≤ 8 S 1 = 1.13(1 + 0.13 χ 2) –1;

● when χ ≤ 8 (F = 1) S 1 = χ (3.58 χ 2 +3.52 χ + 120) –1 ;

● when χ ≤ 8 (F = 1) S 1 = (0.1 χ 2 +2.47 χ + 17.8) – 1 .

Practical part

The laboratory report must contain:

1) initial data;

2) the results of all calculations;

3) conclusions.

Control questions

1. What are man-made emissions?
2. Heat sources and their role in environmental pollution.
3. The influence of metallurgical and chemical processes on environmental pollution.
4. What causes the destruction of the ozone layer?
5. What causes acid precipitation?
6. What is the greenhouse effect and what is its danger?
7. What is the cause of air pollution?
8. Environmental protection / Ed. S.V. Belova. M.: Higher School, 1991. 2. 234 p.
9. Ecology / Ed. Denisova V.V.: Rostov-on-Don, MarT, 2002, 630 p.
10. Fedorova A.I. Workshop on ecology and environmental protection. M.: VLADOS, 2001, 288 p.

Noise– these are any sounds that disturb the silence or irritate a person and interfere with the perception of useful signals. The irritating effect of noise is a significant factor influencing the functional state of the cerebral cortex and central nervous system, and through them, the entire body as a whole.

It is estimated that in the US, noise losses at work are around $4 million per year, and in the UK they are higher than those caused by fires. In large cities, noise shortens life by 8-12 years.

The human ear perceives sounds with a frequency of 20 to 20,000 Hz. Below this limit lies infrasound, above – ultrasound. The human ear is most sensitive in the frequency range from 1,000 to 4,000 Hz.

Noise is usually measured on the “A” characteristic of a sound level meter. This characteristic adjusts the frequency sensitivity of the sound level meter in accordance with the characteristics of the human hearing system, that is, it reflects the physiological effect of sound on the body. The resulting value is called sound level, the unit of measurement is decibel “A” (dBA). This characteristic is international and in Russia is enshrined in GOST 12.1.003-83 and sanitary standards SN-2.2.4/2.1.8.582-96. The hearing threshold is at the level of 10 dBA, a sound level of 60-70 dBA has an irritating effect, at 100-110 dBA hearing impairment occurs, and 120-130 dBA is the pain threshold.

The main sources of noise in railway transport are moving trains, track machines and production equipment of enterprises. The noise level on the railway ranges from 66 dBA (with one pair of passenger trains moving per hour) to 91 dBA (30 pairs of freight trains). The locomotive is one of the main sources of noise in a moving train. So, on a diesel locomotive, the noise of a 2D100 diesel engine reaches 115 dBA, the exhaust system - 123 dBA, the traction generator - 99 dBA, the traction motor - 99 dBA, the oil pump - 100 dBA, the fuel pump - 97 dBA, the compressor - 105 dBA. On the VL-10 electric locomotive, the fan sound level is 111 dBA, and the compressor sound level is 108 dBA.

The permissible noise levels for industrial and residential premises are given in table. 8.

Table 8

Acceptable noise levels

Type of room or area	Permissible noise level, dBA
Industrial premises:
educational institutions, research institutes, administrative buildings
premises of design bureaus, technical departments, etc.
observation and remote control cabins without voice communication by telephone
the same with voice communication by telephone
workplaces in workshops, driver's cabins
train stations
Residential development:
living rooms of apartments - from 7 to 23 hours
- from 23 to 7 o'clock
rooms in dormitories - from 7 a.m. to 11 p.m.
- from 23 to 7 o'clock
residential areas - from 7 a.m. to 11 p.m.
- from 23 to 7 o'clock

It is obvious that the permissible noise levels for industrial and residential premises and areas near railway stations, locomotive depots and rolling stock repair plants are significantly exceeded.

Moving trains are also sources of low-frequency (infrasonic) vibrations. Mechanical vibrations created by trains are especially strong when moving through bridges and tunnels. Studies have shown that prolonged exposure to vibration causes functional changes in the central nervous and cardiovascular systems, the consequences of which are a decrease in the speed of human reactions, the development of hypertension, etc.

To reduce noise in railway transport, the following main measures are taken:

Protective afforestation;

Shielding noise sources;

Rational planning of adjacent residential areas near railway facilities;

Installation of mufflers;

Protection by distance.

Green spaces have a noticeable effect on the propagation of noise in the ground space. Colliding with them, part of the energy of the sound wave is reflected as if from a screen, the other (large) part is absorbed. A protective forest belt, the width of which varies from 10 to 30 m, allows you to reduce the noise level by 4 dBA (three rows of deciduous trees) to 11 dBA (five rows of coniferous trees).

The harmful effects of noise on the population can be reduced by placing high-speed railway tracks in tunnels, excavations, and behind slopes of natural or artificial terrain. Here it is possible to use noise barriers made of corrugated steel sheets 3 m high. Such barriers also serve as fencing for the right-of-way. The effectiveness of noise reduction by screening structures is directly proportional to their height and inversely proportional to the distance from the noise source to the screen. Therefore, it is advisable to place the screens as close as possible to the noise source.

Silencers come in two types: active (using sound-absorbing materials - ceramics, mineral wool, etc.) and reactive (based on reflecting sound back to the source or reducing energy). Most mufflers are combined.

However, the main measure of protection against noise, vibration and EMF is protection by distance.

Lesson Objectives

1. General education

Strengthening the ecological focus of biological knowledge; providing students with information about environmental noise pollution and its impact on humans.

Acquisition by students of knowledge of an ethical, humanitarian nature, which forms the basis of their worldview.

Teaching students to independently acquire knowledge in a group form of organizing cognitive activity.

Students mastering the fundamentals of the methodology of scientific knowledge.

2. Developmental

Development of cognitive interest.

Development of logical thinking (analysis, comparison, generalization, definition and explanation of concepts).

Diversified personality development: memory training, observation, stimulation of cognitive interest, creativity, problem analysis skills and ways to solve them.

Development of skills to apply biological knowledge in practice.

3. Educational tasks

Fostering environmental literacy, a sense of collectivism, the formation and development of moral qualities of schoolchildren.

Teaching methods

Partially search (carrying out independent research, business game).

Verbal (heuristic conversation with elements of independent work).

Visual-figurative (tables, illustrations, listening to recordings of noise, excerpts from literary works).

Lesson type: learning new material.

Forms of organization of cognitive activity: individual and group.

Equipment: audio tape recorder, audio cassette with a recording of E. Grieg’s work “Morning”, with noise of natural and anthropogenic origin; information sheets for individual work by students; tables, posters and drawings on the topic of the lesson; mechanical watch and ruler.
In the previous lesson, two students are given the task of conducting a survey of ninth-grade students to find out their attitude towards natural noises (question: “What feelings do natural noises make you feel?”). Before the lesson begins, the class is divided into four groups; On each student's desk there is an information sheet, a mechanical clock and a ruler.

DURING THE CLASSES

1. Teacher's introduction

Quiet music is playing. The teacher reads excerpts from poems about the Earth - the planet of animals, plants and people, the planet, an integral part and main enemy of which is man.

We are small children of one big nature,
We share with her good fortune and adversity,
She and I have the same fate.

My planet is a human home,
But how can she live under a smoky hood,
Where the gutter is the ocean
Where is all of nature caught in a trap?
Where there is no place for either a stork or a lion.
Where the grass groans: “I can’t take it anymore!”

(Conversation with students about the relevance of the problem of environmental protection.)

What are these passages talking about?

The problem of environmental pollution is too complex and multifaceted to try to study it in class. Therefore, we will limit ourselves to a small part of it and get acquainted with one of the types of environmental pollutants. But try to determine which one by listening to an excerpt from B. Vasiliev’s story “Don’t Shoot White Swans.” ( Listening to an excerpt against the background of music by E. Grieg. Student answers.)

Noise generally receives little attention in the media and is not considered by many to be an air pollutant. But is this really so? We will find out this in today's lesson. ( Setting lesson objectives. Students propose lesson objectives, and the teacher displays appropriate banners.)

1. Study noise as one of the environmental pollutants.
2. Identify the effect of noise on the human body.
3. Establish a link between environmental protection and health protection.

Let our motto today be the words of the writer B. Vasiliev: “I need to figure it out myself, and in order to figure it out myself, I need to think together.”

The motto is written on the board. The teacher explains the rules for using the information sheet. The information sheet is pasted into the workbook, on it students write the topic of the lesson, the main concepts of the topic, fill out the table, and write down their homework.

2. Learning new material

Types of noise and their effect on human senses

During a frontal conversation with students, based on the knowledge they previously acquired from a physics course, the concept of noise as a random mixture of sounds of different heights (frequencies) is specified and a classification of noise is given (natural and anthropogenic). When listening to noise and during a frontal conversation, the effect of noise on the human body (on mental processes) is revealed.

During the work, the columns of the table of the working page of the information sheet are filled in.

INFORMATION SHEET

Lesson topic. The effect of noise on the human body

New term:___________________________

The field of ecology at the intersection of bioacoustics and human ecology, which deals with natural and man-made sounds that affect the human psyche and health, as well as the condition and stability of ecosystems.

The teacher summarizes the data obtained and leads the class to the conclusion about the generally beneficial effect of natural noise on the human body.

What do you think makes up the background noise in a modern city?

An audio recording of city noise is listened to, and the following questions are discussed:

– did you like this noise symphony;
– how do you explain your attitude to these noises;
– what kind of noise is there more in the recording and why?

The teacher leads the class to the conclusion that noise affects people differently: their effect depends on the origin of the noise, the volume level, the age and health of the person, and environmental conditions.

The noise volume level depends on the source and is measured in relative units - decibels: 1 dB = 10 log(P1/P2), where the decimal logarithm sign is the ratio of the acoustic power of the noise. Noise can range in volume from 0 dB (the quietest audible sound) to over 160 dB. Sounds louder than 120 dB, i.e. sounds that are one trillion times louder than the quietest audible sounds cause pain. The perception of sound also depends on the pitch. Loud, high-frequency sounds cause the most damage to your hearing (and cause the most stress). The table shows typical or maximum noise levels from various sources.

Using the table posted on the board, students answer the following questions:

– why whispering and leafing through newspapers are harmless to humans;
– how would you rate the noise level during the school day (lessons and breaks) from the point of view of the impact on the body;
– what conclusions can be drawn based on the data in the table?

Table. Sound volume levels from different sources

Changes in the hearing system under the influence of loud sounds

I suggest you answer the question: “Which organ reacts to excessive noise first of all?”

According to statistics, today 20 out of 150 million Russians suffer from hearing loss. A group of scientists examined young people who often listen to loud modern music. In 20% of boys and girls who were excessively fond of rock music, hearing was reduced in the same way as in 85-year-old people.

In groups, a hearing acuity test is carried out (task from the information sheet). The teacher first identifies, through a survey, those who like to listen to loud music with headphones, calm music, and those who like silence, and their hearing acuity is determined.

Determination of hearing acuity

Hearing acuity is the minimum sound volume that can be perceived by the subject's ear.

Equipment: mechanical watch, ruler.

Operating procedure

1. Bring the watch closer to you until you hear a sound. Measure the distance from your ear to the watch in centimeters.
2. Place the watch tightly against your ear and move it away from you until the sound disappears. Again determine the distance to the clock.
3. If the data matches, this will be approximately the correct distance.
4. If the data does not match, then to estimate the hearing distance you need to take the arithmetic average of the two measurements.

Evaluation of test results

Normal hearing would be such that the ticking of an average-sized watch can be heard at a distance of 10–15 cm.

The numbers are written on the board, analyzed, after which the students answer the question: “What changes occur in the hearing aid under the influence of loud sounds?”

Using the “Hearing Analyzer” table, students talk about the conversion of sound signals into electrical signals, point out the changes that occur in the hearing aid during prolonged exposure to loud sounds:

– with constant stretching of the eardrum, its elasticity decreases, so a high volume of sound is required for it to begin to vibrate, i.e. the sensitivity of the auditory analyzer decreases;

– auditory receptors are damaged.

The effect of noise on the human body

But is it only the hearing organs that are affected by noise?

Students are encouraged to find out by reading the following statements about noise by prominent scientists.

1. Noise causes premature aging. In thirty cases out of a hundred, noise reduces the life expectancy of people in large cities by 8–12 years.

2. Every third woman and every fourth man suffer from neuroses caused by increased noise levels.

3. A sufficiently strong noise after 1 minute can cause changes in the electrical activity of the brain, which becomes similar to the electrical activity of the brain in patients with epilepsy.

4. Diseases such as gastritis, stomach and intestinal ulcers are most often found in people living and working in noisy environments. For pop musicians, stomach ulcers are an occupational disease.

5. Noise depresses the nervous system, especially when it is repeated.

6. Under the influence of noise, there is a persistent decrease in the frequency and depth of breathing. Sometimes cardiac arrhythmia and hypertension appear.

7. Under the influence of noise, carbohydrate, fat, protein, and salt metabolisms change, which manifests itself in changes in the biochemical composition of the blood (blood sugar levels decrease).

Brief conclusion from the discussion: excessive noise (above 80 dB) affects not only the hearing organs, but also other organs and systems (circulatory, digestive, nervous, etc.), vital processes are disrupted, energy metabolism begins to prevail over plastic, which leads to premature aging of the body.

Discussion of sociological survey data

Two students in your class conducted a study in the form of a sociological survey to identify the effect of long-term noise on the mental processes of ninth-grade students. I give the floor to them.

The first student presents survey data, from which it follows that long-term noise leads to complaints of fatigue, memory loss, decreased attention, loss of performance, increased irritability, sleep disturbance, and general weakness. The story is accompanied by a demonstration of a colorful pie chart, where all data is presented as a percentage.

According to the second student, exposure to noise can gradually lead to mental illness. As an illustration, a “ladder” folded into an accordion is hung on the board, which gradually unfolds during the story.

Measures to protect people from noise exposure

So noise is harmful. “Noise is a slow killer,” say American experts. But is it possible to reduce its impact on living organisms, including humans? What can each of us do?

Work in groups (organizational game) - development of projects for protecting people from noise exposure at different social levels.

Group I. I am a layman (memo to the layman).

Group II. I am the mayor of the city.

III group. I am an architect.

IV group. I am the director of a large plant.

Groups draw up projects on whatman paper, hang them on the board and defend them.

3. Conclusion

More than once in our lessons we will talk and think about the consequences of human activity for nature and ourselves. I would like to hope that today’s conversation did not go unnoticed for you. We have hardly touched upon the problem of the impact of noise on the environment, and this problem is as complex and multifaceted as the problem of the impact of noise on humans that we discussed. Only by protecting nature from the harmful consequences of our activities can we save ourselves.

If we are destined to breathe the same air,
Let us all unite forever,
Let's save our souls
Then we ourselves will survive on Earth.

N. Starshinov

What conclusions did you draw for yourself after today’s conversation? ( Students' responses are heard.)

4. Checking the assimilation of new material using self-analysis

During the lesson we thought together, but at the same time everyone worked individually. And now you have to evaluate your activities in class.

The teacher explains how to fill out the student’s self-assessment sheet, then plays an audio recording of nature sounds, and the students evaluate their work.

STUDENT SELF-ASSESSMENT SHEET

Noise as an environmental factor.

Tasks:

1. General education

• Strengthening the ecological focus of biological knowledge; providing students with information about environmental noise pollution and its impact on humans.
• Acquisition by students of knowledge of an ethical, humanitarian nature, which forms the basis of their worldview.
• Teaching students to independently acquire knowledge in a group form of organizing cognitive activity.
• Students mastering the fundamentals of the methodology of scientific knowledge.

2. Developmental

• Development of cognitive interest.
• Development of logical thinking (analysis, comparison, generalization, definition and explanation of concepts).
• Diversified personality development: memory training, observation, stimulation of cognitive interest, creativity, problem analysis skills and ways to solve them.
• Development of skills to apply biological knowledge in practice.

3. Educational tasks

• Fostering environmental literacy, a sense of collectivism, the formation and development of moral qualities of schoolchildren.

Teaching methods

• Partially search (carrying out independent research, business game).
• Verbal (heuristic conversation with elements of independent work).
• Visual-figurative (tables, illustrations, listening to recordings of noise, excerpts from literary works).
• Test.

Forms of organization of cognitive activity:individual and group.

Equipment: audio tape recorder, audio cassette with a recording of E. Grieg’s work “Morning”, with noise of natural and anthropogenic origin; information sheets for individual work by students; tables, posters and drawings on the topic of the lesson; mechanical watch and ruler.
In advance, two students are given the task of conducting a survey of 8th and 9th grade students to find out their attitude towards natural noises with the question: “What feelings do natural noises make you feel?” Before the start of the lesson, the children are divided into 4 groups; On each student's desk there is an information sheet, a mechanical clock and a ruler.

Progress of the lesson

1. Introductory speech by the teacher.

Quiet music is playing. The teacher reads excerpts from poems about the Earth - the planet of animals, plants and people, the planet of which man is an integral part and main enemy.

We are small children of one big nature,
We share with her good fortune and adversity,
She and I have the same fate.

My planet is a human home,
But how can she live under a smoky hood,
Where the gutter is the ocean
Where is all of nature caught in a trap?
Where there is no place for either a stork or a lion.
Where the grass groans: “I can’t take it anymore!”

(Conversation with students about the relevance of the problem of environmental protection.)

What are these passages talking about?

The problem of environmental pollution is too complex and multifaceted to try to study it in class. Therefore, we will limit ourselves to a small part of it and get acquainted with one of the types of environmental pollutants. But try to determine which one by listening to an excerpt from B. Vasiliev’s story “Don’t Shoot White Swans.” (Listening to an excerpt against the background of music by E. Grieg. Student answers.)

Noise generally receives little attention in the media and is not considered by many to be an air pollutant. But is this really so? We will find out this in today's lesson. (Voicing the objectives of the lesson, the teacher hangs up the corresponding banners.)

1. Study noise as one of the environmental pollutants.
2. Identify the effect of noise on the human body.
3. Establish a link between environmental protection and health protection.

Let our motto today be the words of the writer B. Vasiliev: “I need to figure it out myself, and in order to figure it out myself, I need to think together.”

(The motto is written on the board. The teacher explains the rules for working with the information sheet. The information sheet is pasted into the workbook, on it students write the topic of the lesson, the basic concepts of the topic, fill out the table, write down assignments).

2. Studying new material.

Types of noise and their effect on human senses

During a conversation with students, based on the knowledge they previously acquired from a physics course, the concept of noise as a random mixture of sounds of different heights (frequencies) is specified, and a classification of noise is given (natural and anthropogenic). When listening to noise and during a frontal conversation, the effect of noise on the human body (on mental processes) is revealed.

During the work, the columns of the table of the working page of the information sheet are filled in.

INFORMATION SHEET

Topic of the lesson.

New term:___________________________

The field of ecology at the intersection of bioacoustics and human ecology, which deals with natural and man-made sounds that affect the human psyche and health, as well as the condition and stability of ecosystems.

The teacher summarizes the data obtained and leads the class to the conclusion about the generally beneficial effect of natural noise on the human body.

What do you think makes up the background noise in a modern city?

(An audio recording of city noise is listened to.) The following issues are being discussed:

– did you like this noise symphony;
– how do you explain your attitude to these noises;
– what kind of noise is there more in the recording and why?

The teacher leads the class to the conclusion that noise affects people differently: their effect depends on the origin of the noise, the volume level, the age and health of the person, and environmental conditions.

The noise volume level depends on the source and is measured in relative units - decibels: 1 dB = 10 log(P1/P2), where the decimal logarithm sign is the ratio of the acoustic power of the noise. Noise can range in volume from 0 dB (the quietest audible sound) to over 160 dB. Sounds louder than 120 dB, i.e. sounds that are one trillion times louder than the quietest audible sounds cause pain. The perception of sound also depends on the pitch. Loud, high-frequency sounds cause the most damage to your hearing (and cause the most stress). The table shows typical or maximum noise levels from various sources.

(Using the chart posted on the board, students answer the following questions.)

– Why whispering and leafing through newspapers are harmless to humans;
– How would you rate the noise level during the school day (lessons and breaks) from the point of view of the impact on the body;
– What conclusions can be drawn based on the data in the table?

Table. Sound volume levels from different sources

Changes in the hearing system under the influence of loud sounds

I suggest you answer the question: “Which organ reacts to excessive noise first of all?”

According to statistics, today 20 out of 150 million Russians suffer from hearing loss. A group of scientists examined young people who often listen to loud modern music. In 20% of boys and girls who were excessively fond of rock music, hearing was reduced in the same way as in 85-year-old people.

(In groups, a test is carried out to determine hearing acuity - a task from the information sheet. The teacher first identifies, as a result of a survey, those who like to listen to loud music with headphones, calm music, those who like silence, and their hearing acuity is determined).

TEST

Determination of hearing acuity

Hearing acuity is the minimum sound volume that can be perceived by the subject's ear.

Equipment: mechanical watch, ruler.

Operating procedure

1. Bring the watch closer to you until you hear a sound. Measure the distance from your ear to the watch in centimeters.
2. Place the watch tightly against your ear and move it away from you until the sound disappears. Again determine the distance to the clock.
3. If the data matches, this will be approximately the correct distance.
4. If the data does not match, then to estimate the hearing distance you need to take the arithmetic mean of the two measurements.

Evaluation of test results

Normal hearing would be such that the ticking of an average-sized watch can be heard at a distance of 10–15 cm.

The numbers are written on the board, analyzed, after which the students answer the question: “What changes occur in the hearing aid under the influence of loud sounds?”

Using the “Hearing Analyzer” table, the guys talk about the conversion of sound signals into electrical signals, point out the changes that occur in the hearing aid during prolonged exposure to loud sounds:

– with constant stretching of the eardrum, its elasticity decreases, so a high volume of sound is required for it to begin to vibrate, i.e. the sensitivity of the auditory analyzer decreases;

– auditory receptors are damaged.

The effect of noise on the human body

But is it only the hearing organs that are affected by noise?

Students are encouraged to find out by reading the following statements about noise by prominent scientists.

1. Noise causes premature aging. In thirty cases out of a hundred, noise reduces the life expectancy of people in large cities by 8–12 years.

2. Every third woman and every fourth man suffer from neuroses caused by increased noise levels.

3. A sufficiently strong noise after 1 minute can cause changes in the electrical activity of the brain, which becomes similar to the electrical activity of the brain in patients with epilepsy.

4. Diseases such as gastritis, stomach and intestinal ulcers are most often found in people living and working in noisy environments. For pop musicians, stomach ulcers are an occupational disease.

5. Noise depresses the nervous system, especially when it is repeated.

6. Under the influence of noise, there is a persistent decrease in the frequency and depth of breathing. Sometimes cardiac arrhythmia and hypertension appear.

7. Under the influence of noise, carbohydrate, fat, protein, and salt metabolisms change, which manifests itself in changes in the biochemical composition of the blood (blood sugar levels decrease).

Brief conclusion from the discussion: excessive noise (above 80 dB) affects not only the hearing organs, but also other organs and systems (circulatory, digestive, nervous, etc.), vital processes are disrupted, energy metabolism begins to prevail over plastic metabolism, which leads to premature aging body.

Discussion of sociological survey data

Two students in your class conducted a study in the form of a sociological survey to identify the effect of long-term noise on the mental processes of ninth-grade students. I give the floor to them.

The first student presents survey data, from which it follows that long-term noise leads to complaints of fatigue, memory loss, decreased attention, loss of performance, increased irritability, sleep disturbance, and general weakness. The story is accompanied by a demonstration of a colorful pie chart, where all data is presented as a percentage.

According to the second student, exposure to noise can gradually lead to mental illness. As an illustration, a “ladder” folded into an accordion is hung on the board, which gradually unfolds during the story.

EFFECT OF NOISE

DIFFICULTIES IN MUTUAL UNDERSTANDING

DISAPPEARANCE OF ATTENTION

LOW CONCENTRATION

ANNOYANCE

LOSS OF SLEEP

IRRITABILITY

REDUCED FUNCTIONAL ACTIVITY

DISCONTENT

DIFFICULTIES IN THE FAMILY

QUARRELING

MENTAL ILLNESSES

Measures to protect people from noise exposure

So noise is harmful. “Noise is a slow killer,” say American experts. But is it possible to reduce its impact on living organisms, including humans? What can each of us do?

Work in groups - development of projects for protecting people from noise exposure at different social levels.

• Group I. I am a layman (memo to the layman).
• Group II. I am the mayor of the city.
• III group. I am an architect.
• IV group. I am the director of a large plant.

Groups draw up projects on whatman paper, hang them on the board and defend them.

3. Conclusion

We will talk and think more than once about the consequences of human activity for nature and ourselves. I would like to hope that today’s conversation did not go unnoticed for you. We have hardly touched upon the problem of the impact of noise on the environment, and this problem is as complex and multifaceted as the problem of the impact of noise on humans that we discussed. Only by protecting nature from the harmful consequences of our activities can we save ourselves.

If we are destined to breathe the same air,
Let us all unite forever,
Let's save our souls
Then we ourselves will survive on Earth.

N. Starshinov

What conclusions did you draw for yourself after today’s conversation? (Students' responses are heard.)

4. Checking the assimilation of new material using self-analysis

During the lesson we thought together, but at the same time everyone worked individually. And now you have to evaluate your activities in class.

The teacher explains how to fill out the student’s self-assessment sheet, then plays an audio recording of nature sounds, and the students evaluate their work.

STUDENT SELF-ASSESSMENT SHEET